#🎜🎜🎜🎜테마: 🎜PHP🎜🎜난이도: ⭐⭐🎜🎜🎜stdClass 그냥 다른 유형을 객체로 캐스팅할 때 사용되는 일반 "빈" 클래스입니다. stdClass는 PHP의 객체에 대한 기본 클래스가 아닙니다. 🎜🎜const FOO = 'BAR';
define('FOO', 'BAR');
// but
if (...) {
const FOO = 'BAR'; // 无效
}
if (...) {
define('FOO', 'BAR'); // 有效
}로그인 후 복사
로그인 후 복사
对于匿名对象，动态属性等很有用。
考虑 StdClass 的一种简单使用场景是替代关联数组。请参见下面的示例，该示例显示 json_decode() 如何允许获取 StdClass 实例或关联数组。
同样但未在本示例中显示的 SoapClient::__soapCall 返回一个 StdClass 实例。
//带有StdClass的示例
$json = '{ "foo": "bar", "number": 42 }';
$stdInstance = json_decode($json);
echo $stdInstance - > foo.PHP_EOL; //"bar"
echo $stdInstance - > number.PHP_EOL; //42
//Example with associative array
$array = json_decode($json, true);
echo $array['foo'].PHP_EOL; //"bar"
echo $array['number'].PHP_EOL; //42로그인 후 복사
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? 源自: stackoverflow.com
Q7: PHP 中的 die () 和 exit () 函数有什么不同？#
话题: PHP
困难: ⭐⭐
没有区别，它们是一样的。 选择 die() 而不是 exit() 的唯一好处可能是你节省了额外键入一个字母的时间.
? 源自: stackoverflow.com
Q8: 它们之间的主要区别是什么#
话题: PHP
困难: ⭐⭐
const 和 define 的根本区别在于，const 在编译时定义常量，而 define 在运行时定义常量。
const FOO = 'BAR';
define('FOO', 'BAR');
// but
if (...) {
const FOO = 'BAR'; // 无效
}
if (...) {
define('FOO', 'BAR'); // 有效
}로그인 후 복사
로그인 후 복사
同样在 PHP 5.3 之前，const 命令不能在全局范围内使用。你只能在类中使用它。当你想要设置与该类相关的某种常量选项或设置时，应使用此选项。或者你可能想要创建某种枚举。一个好的 const 用法的例子是摆脱了魔术数字。
Define 可以用于相同的目的，但只能在全局范围内使用。它应该仅用于影响整个应用程序的全局设置。
除非你需要任何类型的条件或表达式定义，否则请使用 consts 而不是 define()—— 这仅仅是为了可读性！
? 源自: stackoverflow.com
Q9: isset () 和 array_key_exists () 之间有什么区别？#
话题: PHP
困难: ⭐⭐
array_key_exists 它会告诉你数组中是否存在键，并在 $a 不存在时报错。- 如果 key 或变量存在且不是
null，isset 才会返回 true。当 $a 不存在时，isset 不会报错。
考虑:
$a = array('key1' => 'Foo Bar', 'key2' => null);
isset($a['key1']); // true
array_key_exists('key1', $a); // true
isset($a['key2']); // false
array_key_exists('key2', $a); // true
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? 源自: stackoverflow.com
Q10: var_dump () 和 print_r () 有什么不同？#
话题: PHP
困难: ⭐⭐
考虑:
$obj = (object) array('qualitypoint', 'technologies', 'India');
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var_dump($obj) 将在屏幕的输出下方显示:
object(stdClass)#1 (3) {
[0]=> string(12) "qualitypoint"
[1]=> string(12) "technologies"
[2]=> string(5) "India"
}로그인 후 복사
stdClass Object (
[0] => qualitypoint
[1] => technologies
[2] => India
)
로그인 후 복사
? 源自: stackoverflow.com
Q11: 解释不同的 PHP 错误是什么#
话题: PHP
困难: ⭐⭐
notice 不是一个严重的错误，它说明执行过程中出现了一些错误，一些次要的错误，比如一个未定义的变量。- 当出现更严重的错误，如 include () 命令引入不存在的文件时，会给出警告
warning。 这个错误和上面的错误发生，脚本都将继续。 fatal error 致命错误将终止代码。未能满足 require () 将生成这种类型的错误。
? 源自: pangara.com
Q12: 如何在 PHP 中启用错误报告？
话题: PHP
困难: ⭐⭐
检查 php.ini 中的 “display_errors” 是否等于 “on”，或者在脚本中声明 “ini_set('display_error',1)”。
然后，在你的代码中包含 “ERROR_REPORTING(E_ALL)”，以便在脚本执行期间显示所有类型的错误消息。
? 源自: codementor.io
Q13: 使用默认参数声明某些函数
话题: PHP
困难: ⭐⭐
思考:
function showMessage($hello = false){
echo ($hello) ? 'hello' : 'bye';
}로그인 후 복사
? 源自: codementor.io
Q14: PHP 是否支持多重继承？
话题: PHP
困难: ⭐⭐
PHP 只支持单一继承；这意味着使用关键字’extended’只能从一个类扩展一个类。
? 源自: guru99.com
Q15: 在 PHP 中，对象是按值传递还是按引用传递？
话题: PHP
困难: ⭐⭐
在 PHP 中，通过值传递的对象。
? 源自: guru99.com
Q16:$a != $b 和 $a !== $b ，之间有什么区别？
话题: PHP
困难: ⭐⭐
!= 表示 不等于 (如果 $a 不等于 $b，则为 True)， !== 表示 不全等 (如果 $a 与 $b 不相同，则为 True).
? 源自: guru99.com
Q17: 在 PHP 中，什么是 PDO？
话题: PHP
困难: ⭐⭐
PDO 代表 PHP 数据对象。
它是一组 PHP 扩展，提供核心 PDO 类和数据库、特定驱动程序。它提供了供应商中立、轻量级的数据访问抽象层。因此，无论我们使用哪种数据库，发出查询和获取数据的功能都是相同的。它侧重于数据访问抽象，而不是数据库抽象。
? 源自: github.com/Bootsity
Q18: 说明我们如何在 PHP 中处理异常？
Topic: PHP
Difficulty: ⭐⭐
当程序执行出现异常报错时，后面的代码将不会再执行，这时 PHP 将会尝试匹配第一个 catch 块进行异常的处理，如果没有捕捉到异常程序将会报致命错误并显示”Uncaught Exception”。
可以在 PHP 中抛出和捕获异常。
为了处理异常，代码可以被包围在”try” 块中.
每个 try 必须至少有一个对应的 catch 块 。多个不同的 catch 块可用于捕获不同类的异常。
在 catch 块中也可以抛出异常（或重新抛出之前的异常）。
思考:
try {
print "this is our try block n";
throw new Exception();
} catch (Exception $e) {
print "something went wrong, caught yah! n";
} finally {
print "this part is always executed n";
}로그인 후 복사
? Source: github.com/Bootsity
Q19: 区分 echo 和 print ()
Topic: PHP
Difficulty: ⭐⭐
echo 和 print 基本上是一样的。他们都是用来打印输出数据的。
区别在于:
- echo 没有返回值，而 print 的返回值为 1，因此 print 可以在表达式中使用。
- echo 可以接受多个参数一起输出 (但是这种多个的输出方式很少见)，而 print 一次只可以输出一个参数。
- echo 的输出比 print 效率要高一些 .
? Source: github.com/Bootsity
Q20: require_once 和 require 在什么场景下使用？
Topic: PHP
Difficulty: ⭐⭐⭐
require_once() 作用与 require() 的作用是一样的，都是引用或包含外部的一个 php 文件，require_once() 引入文件时会检查文件是否已包含，如果已包含，不再包含 (require) 它。
我建议在 99.9% 的时候要使用 require_once
使用 require 或 include 意味着您的代码不可在其他地方重用，即您要拉入的脚本实际上是在执行代码，而不是提供类或某些函数库。
? Source: stackoverflow.com
Q21: 判断 PHP 数组是否是关联数组
Topic: PHP
Difficulty: ⭐⭐⭐
思考:
function has_string_keys(array $array) {
return count(array_filter(array_keys($array), 'is_string')) > 0;
}로그인 후 복사
如果 $array 至少有一个字符串类型的 key ，它将被视为关联数组。
? Source: stackoverflow.com
Q22: 如何将变量和数据从 PHP 传至 Javascript
Topic: PHP
Difficulty: ⭐⭐⭐
这里有几种实现方法：
思考 get-data.php:
echo json_encode(42);
로그인 후 복사
思考 index.html:
<script>
function reqListener () {
console.log(this.responseText);
}
var oReq = new XMLHttpRequest(); // new 一个请求对象
oReq.onload = function() {
// 在这里你可以操作响应数据
// 真实的数据来自 this.responseText
alert(this.responseText); // 将提示: 42
};
oReq.open("get", "get-data.php", true);
// ^ 不要阻塞的其余部分执行。
// 不要等到请求结束再继续。
oReq.send();
</script>로그인 후 복사
- 可以在网页任何地方输出数据，然后使用 JavaScript 从 DOM 中获取信息.
<div id="dom-target" style="display: none;">
<?php
$output = "42"; // 此外, 做一些操作，获得 output.
echo htmlspecialchars($output); /* 你必须避免特殊字符，不然结果将是无效HTML。 */
?>
</div>
<script>
var div = document.getElementById("dom-target");
var myData = div.textContent;
</script>로그인 후 복사
- 直接在 JavaScript 代码中 echo 数据。
<script>
var data = <?php echo json_encode("42", JSON_HEX_TAG); ?>; // Don't forget the extra semicolon!
</script>로그인 후 복사
? Source: stackoverflow.com
Q23: 有一个方法可以复制一个 PHP 数组至另一个数组吗？
Topic: PHP
Difficulty: ⭐⭐⭐
PHP 数组通过复制进行赋值，而对象通过引用进行赋值。所有默认情况下，PHP 将复制这个数组。这里有一个 PHP 参考，一目了然：
$a = array(1,2);
$b = $a; // $b 是一个不同的数组
$c = &$a; // $c 是 $a 的引用
로그인 후 복사
? Source: stackoverflow.com
Q24: What will be returned by this code?
Topic: PHP
Difficulty: ⭐⭐⭐
Consider the code:
$a = new stdClass();
$a->foo = "bar";
$b = clone $a;
var_dump($a === $b);
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What will be echoed to the console?
Two instances of the same class with equivalent members do NOT match the === operator. So the answer is:
? Source: stackoverflow.com
Q25: What will be returned by this code? Explain the result.
Topic: PHP
Difficulty: ⭐⭐⭐
Consider the code. What will be returned as a result?
$something = 0;
echo ('password123' == $something) ? 'true' : 'false';
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The answer is true. You should never use == for string comparison. Even if you are comparing strings to strings, PHP will implicitly cast them to floats and do a numerical comparison if they appear numerical. === is OK.
For example
'1e3' == '1000' // true
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also returns true.
? Source: stackoverflow.com
Q26: What exactly is the the difference between array_map, array_walk and array_filter?
Topic: PHP
Difficulty: ⭐⭐⭐
array_walk takes an array and a function F and modifies it by replacing every element x with F(x).array_map does the exact same thing except that instead of modifying in-place it will return a new array with the transformed elements.array_filter with function F, instead of transforming the elements, will remove any elements for which F(x) is not true
? Source: stackoverflow.com
Q27: Explain the difference between exec() vs system() vs passthru()?
Topic: PHP
Difficulty: ⭐⭐⭐
exec() is for calling a system command, and perhaps dealing with the output yourself.system() is for executing a system command and immediately displaying the output - presumably text.passthru() is for executing a system command which you wish the raw return from - presumably something binary.
? Source: stackoverflow.com
Q28: How would you create a Singleton class using PHP?
Topic: PHP
Difficulty: ⭐⭐⭐
/**
* Singleton class
*
*/
final class UserFactory {
/**
* Call this method to get singleton
*
* @return UserFactory
*/
public static
function Instance() {
static $inst = null;
if ($inst === null) {
$inst = new UserFactory();
}
return $inst;
}
/**
* Private ctor so nobody else can instantiate it
*
*/
private
function __construct() {
}
}로그인 후 복사
To use:
$fact = UserFactory::Instance();
$fact2 = UserFactory::Instance();
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But:
$fact = new UserFactory()
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Throws an error.
? Source: stackoverflow.com
Q29: What is the difference between PDO’s query() vs execute()?
Topic: PHP
Difficulty: ⭐⭐⭐
query runs a standard SQL statement and requires you to properly escape all data to avoid SQL Injections and other issues.execute runs a prepared statement which allows you to bind parameters to avoid the need to escape or quote the parameters. execute will also perform better if you are repeating a query multiple times.
Best practice is to stick with prepared statements and execute for increased security. Aside from the escaping on the client-side that it provides, a prepared statement is compiled on the server-side once, and then can be passed different parameters at each execution.
? Source: stackoverflow.com
Q30: What is use of Null Coalesce Operator?
Topic: PHP
Difficulty: ⭐⭐⭐
Null coalescing operator returns its first operand if it exists and is not NULL. Otherwise it returns its second operand.
Example:
$name = $firstName ?? $username ?? $placeholder ?? "Guest";
로그인 후 복사
? Source: github.com/Bootsity
Q31: Differentiate between exception and error
Topic: PHP
Difficulty: ⭐⭐⭐
- Recovering from
Error is not possible. The only solution to errors is to terminate the execution. Where as you can recover from Exception by using either try-catch blocks or throwing exception back to caller. - You will not be able to handle the
Errors using try-catch blocks. Even if you handle them using try-catch blocks, your application will not recover if they happen. On the other hand, Exceptions can be handled using try-catch blocks and can make program flow normal if they happen. Exceptions are related to application where as Errors are related to environment in which application is running.
? Source: github.com/Bootsity
Q32: What are the exception class functions?
Topic: PHP
Difficulty: ⭐⭐⭐
There are following functions which can be used from Exception class.
getMessage() − message of exceptiongetCode() − code of exceptiongetFile() − source filenamegetLine() − source linegetTrace() − n array of the backtrace()getTraceAsString() − formated string of traceException::__toString gives the string representation of the exception.
? Source: github.com/Bootsity
Q33: Differentiate between parameterised and non parameterised functions
Topic: PHP
Difficulty: ⭐⭐⭐
- Non parameterised functions don’t take any parameter at the time of calling.
- Parameterised functions take one or more arguments while calling. These are used at run time of the program when output depends on dynamic values given at run time There are two ways to access the parameterised function:
? Source: github.com/Bootsity
Q34: Explain function call by reference
Topic: PHP
Difficulty: ⭐⭐⭐
In case of call by reference, actual value is modified if it is modified inside the function. In such case, we need to use & symbol with formal arguments. The & represents reference of the variable.
Example:
function adder(&$str2) {
$str2 .= 'Call By Reference';
}
$str = 'This is ';
adder($str);
echo $str;로그인 후 복사
Output:
This is Call By Reference
로그인 후 복사
? Source: github.com/Bootsity
Q35: Why do we use extract()?
Topic: PHP
Difficulty: ⭐⭐⭐
The extract() function imports variables into the local symbol table from an array.
This function uses array keys as variable names and values as variable values. For each element it will create a variable in the current symbol table.
This function returns the number of variables extracted on success.
Example:
$a = "Original";
$my_array = array("a" => "Cat","b" => "Dog", "c" => "Horse");
extract($my_array);
echo "\$a = $a; \$b = $b; \$c = $c";
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Output:
$a = Cat; $b = Dog; $c = Horse
로그인 후 복사
? Source: github.com/Bootsity
Q36: explain what is a closure in PHP and why does it use the “use” identifier?
Topic: PHP
Difficulty: ⭐⭐⭐⭐
Consider this code:
public function getTotal($tax)
{
$total = 0.00;
$callback =
function ($quantity, $product) use ($tax, &$total)
{
$pricePerItem = constant(__CLASS__ . "::PRICE_" .
strtoupper($product));
$total += ($pricePerItem * $quantity) * ($tax + 1.0);
};
array_walk($this->products, $callback);
return round($total, 2);
}로그인 후 복사
Could you explain why use it?
This is how PHP expresses a closure. Basically what this means is that you are allowing the anonymous function to “capture” local variables (in this case, $tax and a reference to $total) outside of it scope and preserve their values (or in the case of $total the reference to $total itself) as state within the anonymous function itself.
A closure is a separate namespace, normally, you can not access variables defined outside of this namespace.
use allows you to access (use) the succeeding variables inside the closure.use is early binding. That means the variable values are COPIED upon DEFINING the closure. So modifying $tax inside the closure has no external effect, unless it is a pointer, like an object is.- You can pass in variables as pointers like in case of
&$total. This way, modifying the value of $total DOES HAVE an external effect, the original variable’s value changes.
? Source: stackoverflow.com
Q37: What exactly are late static bindings in PHP?
Topic: PHP
Difficulty: ⭐⭐⭐⭐
Basically, it boils down to the fact that the self keyword does not follow the same rules of inheritance. self always resolves to the class in which it is used. This means that if you make a method in a parent class and call it from a child class, self will not reference the child as you might expect.
Late static binding introduces a new use for the static keyword, which addresses this particular shortcoming. When you use static, it represents the class where you first use it, ie. it ‘binds’ to the runtime class.
Consider:
class Car {
public static
function run() {
return static::getName();
}
private static
function getName() {
return 'Car';
}
}
class Toyota extends Car {
public static
function getName() {
return 'Toyota';
}
}
echo Car::run(); // Output: Car
echo Toyota::run(); // Output: Toyota로그인 후 복사
? Source: stackoverflow.com
Q38: How to measure execution times of PHP scripts?
Topic: PHP
Difficulty: ⭐⭐⭐⭐
I want to know how many milliseconds a PHP while-loop takes to execute. Could you help me?
You can use the microtime function for this.
Consider:
$start = microtime(true);
while (...) {
}
$time_elapsed_secs = microtime(true) - $start;로그인 후 복사
? Source: stackoverflow.com
Q39: What is the best method to merge two PHP objects?
Topic: PHP
Difficulty: ⭐⭐⭐⭐
//We have this:
$objectA->a;
$objectA->b;
$objectB->c;
$objectB->d;
//We want the easiest way to get:
$objectC->a;
$objectC->b;
$objectC->c;
$objectC->d;
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This works:
$obj_merged = (object) array_merge((array) $obj1, (array) $obj2);
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You may also use array_merge_recursive to have a deep copy behavior.
One more way to do that is:
foreach($objectA as $k => $v) $objectB->$k = $v;
로그인 후 복사
This is faster than the first answer in PHP versions < 7 (estimated 50% faster). But in PHP >= 7 the first answer is something like 400% faster.
? Source: stackoverflow.com
Q40: Compare mysqli or PDO - what are the pros and cons?
Topic: PHP
Difficulty: ⭐⭐⭐⭐
Let’s name some:
PDO is the standard, it’s what most developers will expect to use.
Moving an application from one database to another isn’t very common, but sooner or later you may find yourself working on another project using a different RDBMS. If you’re at home with PDO then there will at least be one thing less to learn at that point.
A really nice thing with PDO is you can fetch the data, injecting it automatically in an object.
PDO has some features that help agains SQL injection
In sense of speed of execution MySQLi wins, but unless you have a good wrapper using MySQLi, its functions dealing with prepared statements are awful. inserts - almost equal, selects - mysqli is2.5% faster for non-prepared statements/6.7% faster for prepared statements.
? Source: stackoverflow.com
Q41: What is use of Spaceship Operator?
Topic: PHP
Difficulty: ⭐⭐⭐⭐
This <=> operator will offer combined comparison in that it will:
- Return 0 if values on either side are equal
- Return 1 if value on the left is greater
- Return -1 if the value on the right is greater
Consider:
//Comparing Integers
echo 1 &lt;= &gt; 1; //outputs 0
echo 3 &lt;= &gt; 4; //outputs -1
echo 4 &lt;= &gt; 3; //outputs 1
//String Comparison
echo &quot;x&quot; &lt;= &gt; &quot;x&quot;; // 0
echo &quot;x&quot; &lt;= &gt; &quot;y&quot;; //-1
echo &quot;y&quot; &lt;= &gt; &quot;x&quot;; //1
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? Source: github.com/Bootsity
Q42: Does PHP have threading?
Topic: PHP
Difficulty: ⭐⭐⭐⭐
Standard php does not provide any multithreading but there is an (experimental) extension that actually does - pthreads. The next best thing would be to simply have one script execute another via CLI, but that’s a bit rudimentary. Depending on what you are trying to do and how complex it is, this may or may not be an option.
? Source: github.com/Bootsity
Q43: Is PHP single or multi threaded?
Topic: PHP
Difficulty: ⭐⭐⭐⭐
PHP is not single threaded by nature. It is, however, the case that the most common installation of PHP on unix systems is a single threaded setup, as is the most common Apache installation, and nginx doesn’t have a thread based architecture whatever. In the most common Windows setup and some more advanced unix setups, PHP can and does operate multiple interpreter threads in one process.
PHP as an interpreter had support for multi-threading since the year 2000.
? Source: github.com/Bootsity
Q44: Provide some ways to mimic multiple constructors in PHP
Topic: PHP
Difficulty: ⭐⭐⭐⭐⭐
It’s known you can’t put two __construct functions with unique argument signatures in a PHP class but I’d like to do something like this:
class Student
{
protected $id;
protected $name;
// etc.
public function __construct($id){
$this-&gt;id = $id;
// other members are still uninitialised
}
public function __construct($row_from_database){
$this-&gt;id = $row_from_database-&gt;id;
$this-&gt;name = $row_from_database-&gt;name;
// etc.
}
}로그인 후 복사
What is the best way to achieve this in PHP?
I’d probably do something like this:
class Student
{
public function __construct() {
// allocate your stuff
}
public static function withID( $id ) {
$instance = new self();
$instance-&gt;loadByID( $id );
return $instance;
}
public static function withRow( array $row ) {
$instance = new self();
$instance-&gt;fill( $row );
return $instance;
}
protected function loadByID( $id ) {
// do query
$row = my_awesome_db_access_stuff( $id );
$this-&gt;fill( $row );
}
protected function fill( array $row ) {
// fill all properties from array
}
}로그인 후 복사
Then if i want a Student where i know the ID:
$student = Student::withID( $id );
로그인 후 복사
Technically you’re not building multiple constructors, just static helper methods, but you get to avoid a lot of spaghetti code in the constructor this way.
Another way is to use the mix of factory and fluent style:
class Student
{
protected $firstName;
protected $lastName;
// etc.
/**
* Constructor
*/
public function __construct() {
// allocate your stuff
}
/**
* Static constructor / factory
*/
public static function create() {
$instance = new self();
return $instance;
}
/**
* FirstName setter - fluent style
*/
public function setFirstName( $firstName) {
$this-&gt;firstName = $firstName;
return $this;
}
/**
* LastName setter - fluent style
*/
public function setLastName( $lastName) {
$this-&gt;lastName = $lastName;
return $this;
}
}
// create instance
$student= Student::create()-&gt;setFirstName(&quot;John&quot;)-&gt;setLastName(&quot;Doe&quot;);로그인 후 복사
? Source: stackoverflow.com
Q45: How could we implement method overloading in PHP?
Topic: PHP
Difficulty: ⭐⭐⭐⭐⭐
You cannot overload PHP functions. Function signatures are based only on their names and do not include argument lists, so you cannot have two functions with the same name.
You can, however, declare a variadic function that takes in a variable number of arguments. You would use func_num_args() and func_get_arg() to get the arguments passed, and use them normally.
Consider:
function myFunc() {
for ($i = 0; $i &lt; func_num_args(); $i++) {
printf(&quot;Argument %d: %s\n&quot;, $i, func_get_arg($i));
}
}
/*
Argument 0: a
Argument 1: 2
Argument 2: 3.5
*/
myFunc(&amp;#39;a&amp;#39;, 2, 3.5);로그인 후 복사
? Source: github.com/Bootsity
为了处理异常，代码可能被包围在一个 try 块中。
每个 try 必须至少有一个提示。
原文地址：https://dev.to/fullstackcafe/45-important-php-interview-questions-that-may-land-you-a-job-1794
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